Conventionally, a CCD (charge coupled device) has been widely used as an image capturing element for a digital camera or video camera. The CCD has a structure in which a large number of photoelectric conversion elements are arranged, for example, in a grid pattern. When receiving light, the photoelectric conversion elements generate electrical charges in accordance with an intensity of the light, and the generated electrical charges are read out sequentially, whereby an image of a subject can be converted into electrical signals.
In order to obtain a color image using the CCD, a color filter containing plural primary color components is applied on a light receiving surface side of the image capturing element, so that light with a predetermined primary color component is inputted into the respective photoelectric conversion elements, whereby an image signal of a color component corresponding to each pixel can be obtained. As the filter used in this case, a Bayer matrix using a filter for each color of R (red), G (green) and B (blue) is well known.
With the image capturing element using the filter with the Bayer matrix, each photoelectric conversion element can obtain only the signal of a color component corresponding to the applied color filter. For example, the photoelectric conversion element covered with the filter for R cannot provide signals of G and B. Therefore, for each pixel, data concerning a primary color component that cannot be obtained directly from the photoelectric conversion elements can be obtained by implementing interpolation process using primary color component data of adjacent pixels having said primary color component. This makes it possible to obtain color image data of the subject for each pixel by using one image capturing element.
When image-capturing is performed by using the filter with the Bayer matrix, it has been known that a false color appears at a portion that contains a high-frequency spatial frequency component in the image of the subject. To deal with this, in general, a process of obscuring the false color is implemented for a region that contains the high frequency component, such that color-difference is reduced and the chroma is suppressed. However, through the suppression of chroma, a so-called “color omission” is likely to occur. In particular, the “color omission” is visually remarkable in a high chroma region, and makes the captured image unnatural.
In view of the facts described above, there has been disclosed a technique of suppressing the false color in a low chroma region while reducing the color omission in the high chroma region (see, for example, Japanese Patent No. 3633561). According to Japanese Patent No. 3633561, an image signal represented in a color space having three primary color components is converted into an image signal represented in a YCbCr color space having a brightness signal Y, color difference signals Cr (=R−Y) and Cb (=B−Y) (R and B represent image signals of a red color component and a blue color component, respectively). The degree of the high frequency component that the brightness signal has in the vicinity of each image is detected on the basis of the brightness signal Y, and the chroma is obtained on the basis of the color difference signals Cb and Cr to detect the low chroma region. With this process, the color difference signals are suppressed for a pixel in the detected low chroma region in accordance with the degree of the high frequency component, and the color difference signals are not suppressed (or is reduced) for the pixel in the high chroma region.